Vertical align of mixed panel?
You understand the formatting wrong - see this with comments:

        # simple label
        layout.label(text=" Simple Row:")

        # create column to be able to merge vertically with align=true on a column
        col = layout.column(align=True)

        # create test row inside the column
        row = col.row(align=True)
        row.prop(scene, "test")
        # even if there is only 1 item in this row it needs aligning because otherwise the column align would'n work

        # create the test2 row within column and allow horizontal merge with align=true on this row
        row = col.row(align=True)
        # we don't want to put anything else on this row other than the 'split' item
        split = row.split(align=True, percentage=0.7)

        # put 2 things inside the split
        split.prop(scene, "test2")
        split.operator("render.render")




You can also make the button span across 2 rows if you order the elements in a different way:

        # simple label
        layout.label(text=" Simple Row:")

        # start with a splitted row - we dont want to split the whole layout if something
        # needs to be added after these elements
        row = layout.row(align=True)
        split = row.split(align=True, percentage=0.7)

        # put 2 columns inside the split
        colA = split.column(align=True)
        colB = split.column(align=True)

        # fill first column with props
        colA.prop(scene, "test")
        colA.prop(scene, "test2")

        # put a row into second column
        row = colB.row(align=True)
        # adjust the row's Y scale
        row.scale_y = 2
        row.operator("render.render")